Tofu, fried bean-curd and soymilk that is their mother liquor, are traditional health food products having soybeans used as the raw material and rich in nutrients. In recent years, tofu or fried bean-curd that is a natural food and soymilk that is their mother liquor have attracted lots of attention among health-conscious consumers.
In order to produce soymilk, soybeans are soaked in water overnight to sufficiently absorb the water and ground down by friction, with water added thereto, to produce a soybean soup that is heated with a heating unit and separated with an extracting unit into soymilk and bean curd refuse. Tofu produced from soymilk having many specks (minute soy fibers) mixed therein in the separating step exhibits a gritty and powdery mouthfeel and little elasticity to deteriorate the flavor and eating texture tofu has to possess per se, and fried bean-curd produced from such tofu prevents tofu dough from being elongated and deteriorates its surface layer stretching. For these reasons, a conventional extracting unit performs natural filtration (gravity filtration: spontaneous) so as not to mix specks in soymilk under pressure forcibly applied to a soybean soup (Patent Document 1, for example). However, the natural filtration results in low extractability of soymilk and large raw-material waste. On the other hand, forcible filtration entails a problem that specks are mixed in extracted soymilk to deteriorate the flavor of the soymilk.
Since soymilk still containing foam is poor to react with bittern (Nigari), makes a coagulating period of time long and is difficult to produce fine tofu, Patent Document 2 discloses a process for producing soymilk for handmade tofu, comprising subjecting a heated soybean soup to primary defoaming using a defoaming unit, extracting the soybean soup using a pressure extracting unit to separate it into soymilk and bean curd refuse (Okara), introducing the soymilk extracted with the pressure application extracting unit into a speck remover to filtrate the soymilk, and subjecting the filtered soymilk to secondary defoaming using a vacuum pan.
Patent Document 1: Japanese Patent No. 3392322
Patent Document 2: JP-A HEI 8-242801
Patent Document 3: JP-A 2002-306104
Patent Document 4: JP-A 2003-245503